When one target of a
#pragma multi rule has a separately declared
dependency, then that dependency must specify the same target set as the
rule. Otherwise there could easily be different prerequisite lists
triggering the same rule, depending on which target is considered.
If the prerequisite lists of different targets of a
rule were allowed to differ, then it would be unclear which
prerequisites trigger the commands in that rule. By requiring the same
target set in a separate dependency specification, a pattern of usage is
enforced that makes it clear which prerequisites trigger the commands in
#pragma multi rule.
For uniformity this rule is enforced even if no commands are mentioned explicitly.